A mobile communications system refers generally to any telecommunications system which enables wireless communication within the service area of the system. A typical mobile communications system is a Public Land Mobile Network (PLMN). Often the mobile communications network is an access network providing a user with wireless access to external networks, hosts, or services offered by specific wireless service providers. In most cases, the user has a subscriber's profile that is held in a Home Public Land Mobile Network (HPLMN). When the user roams to other networks, i.e., a Visited Public Land Mobile Network (VPLMN), calls to that user are first routed to the HPLMN and then forwarded to the VPLMN so the user can receive the call.
In Global System for Mobile communications (GSM), the term mobile station is used to refer to a combination of mobile equipment, i.e., a wireless telephone, and a Subscriber Identification Module (SIM). The SIM allows a user to subscribe to services offered by a wireless service provider, regardless of specific mobile equipment. The mobile equipment is identified by an International Mobile Equipment Identity (IMEI). The SIM includes an International Mobile Subscriber Identity (IMSI) to identify the user to the wireless service provider and provides a secret key for authentication. The IMEI and IMSI are independent, therefore allowing a SIM and its corresponding IMSI to be inserted into different mobile equipment.
One feature available on many of today's mobile stations is a contact list. A contact list allows a user to store names, telephone numbers, physical addresses, email addresses, and other relevant contact information. Most often, a user is given the option to store contact information in a memory of the mobile equipment and/or on the SIM. If a user chooses to store contact information on the SIM, then the contact information can be easily transported to different mobile equipment. If a user chooses to store contact information in the mobile equipment's memory, then the contact information is only available on that mobile equipment. Moreover, the quantity of contacts and type of contact information capable of being stored in the mobile equipment's memory is usually larger and different than that of the SIM. Mobile equipment memory allows a user to assign and store ring tones, graphics, and other personalization features to each contact in the user's contact list. The SIM allows a user to store name, number, email address, and physical address information.
Another feature available on many of today's mobile stations is instant messaging. Instant messaging is a real-time message exchange service. A common feature of instant messaging clients is the ability to populate and maintain a list of contacts. A user can be alerted when a contact from the user's list comes online, and the list of contacts can indicate which of the contacts are currently available for interactive communication. Today, instant messaging is available on cellular telephones and other mobile devices. Instant messaging can be used to send mobile-to-mobile, computer-to-mobile, and mobile-to-computer messages.
The features described above provide users a way to maintain contact information for and to communicate with contacts in a mobile communication system. However, current mobile communication systems do not allow a user's telephone contact list to provide information regarding the availability of a specific contact for communicating via a voice call. Therefore, a heretofore unaddressed need exists to provide a system and method for providing availability information to mobile station users within a mobile communication system.